[4-(3-Amino-4-mehoxy-5-methylphenyl)-1-oxo-1H-phthalaz-2-yl] acetic acid hydrazide and its synergetic effect with KI as a novel inhibitor for low carbon steel corrosion in 0.5 M H2SO4

We report the synthesis of novel [4-(3-amino-4-mehoxy-5-methyl phenyl)-1-oxo-1H-phthalaz-2-yl] acetic acid hydrazide (APPH), followed by its characterization using X-ray diffraction (XRD), Fourier transforms infrared (FT-IR) spectroscopy, 1H-NMR spectroscopy, and LC/MS. Further, the inhibition effect of the varying concentration of APPH on the corrosion of low steel (LCS) in 0.5 M H2SO4 was investigated by weight loss and electrochemical measurements at 30 °C. The percentage inhibition efficacy of APPH increased with concentration and reached about 84% at 0.5 mM at 30 °C, also rising to 88% after 6 h of exposure. According to the polarization measurements, the investigated APPH works as a mixed-type inhibitor. Furthermore, the synergistic corrosion inhibition mechanism APPH showed that the inhibition efficiency maximizes with increasing inhibitor concentration, and the maximum value was 83% at 0.5 mM APPH. The adsorption of APPH on the LCS surface is more fitting to the Langmuir isotherm model. The free energy value (–ΔG° ads) was 33.3 kJ mol−1. Quantum chemical calculation was applied to APPH and acted as excellent support for the experimental data.

Because not all individual compounds positively affect corrosion inhibition, many studies have been conducted to minimize the corrosion percentage by depending on the phenomenon of synergism through adding halide anions. It has been demonstrated that in acid solutions, halide ions form intermediates on a corroding steel surface, which may inhibit or accelerate iron anodic dissolution by substituting some of the adsorbed OH ions in the anodic process. Authors have proposed various mechanisms to explain the synergistic effect of organic inhibitors and halide ions. These include halide ion accumulation, which attracts the inhibitor molecule to the metal, halide ion and organic ion exchange, co-adsorption of inhibitor and halide ions, and a combination of various scenarios. According to the literature, inhibitor cation adsorption would be maximized on the directed dipoles formed by the halide ions as they first adsorb on the metal surface 31,32 .
As an important section of Theoretical chemistry, Quantum chemical calculations have proven to be an excellent tool for interpreting corrosion inhibition mechanisms [33][34][35][36] . The development of hardware and software of quantum chemical procedures, such as functional density theory (DFT), have recently been required as a quick and strong tool to interpret and explain corrosion inhibition performances of inhibitors problems. This is due to the strong associations found between the corrosion inhibitions effectiveness of maximum compounds and numerous semi-empirical criteria. The importance of the adsorption of inhibitor molecules on substrates in the context of corrosion research has lately increased [37][38][39][40][41][42][43][44][45] .
Further, the goal of this study is to continue our previous study on 4-aryl phthalazinone derivatives, which contain amino or hdrazide moiety to synthesize novel inhibitor 24 . APPH that contains both amino and hydrazide groups was investigated for its corrosion percentage on LCS in 0.5 M H 2 SO 4 using electrochemical impedance spectroscopy (EIS), weight loss (WL), and potentiodynamic polarization (PDP) analyses. Iodide ions' synergistic impact on APPH's inhibitive performance was also discussed. Also measured, discussed, and interpreted were a number of thermodynamic parameters, kinetic parameters, and quantum chemical calculations of density functional theory (DFT) for LCS corrosion at varied concentrations of APPH.
Experimental procedure APPH synthesis and equipment. Opti Melt equipment (a melting point automated system with digital image) was used to measure the melting points and are uncorrected. Thin layer chromatography (TLC) on silica gel plates 60-F254 (Merck, 0.25 thickness layer) was used to determine the products' purity and monitor the reactions. Infra-red spectra FTIR were recorded on Bruker Model Vertex 70 with Platinum ATR unit. 1  The steel was mechanically cut in standard cylindrical coupons with a total surface area of 4.08 cm 2 and used for weight loss measurements; Teflon covered other cylindrical coupons, and only one exposed surface with an exposed area of 0.64 cm 2 for the electrochemical study. Then, samples were polished using SiC paper of various grades (#220 to #1200), washed with double-distilled water, degreased with acetone in an ultrasonic bath for 5 minutes, and air-dried before use. The pure H 2 SO 4 of 98 percent analytical quality was used to create the corrosive medium containing 0.5 mol L −1 of H 2 SO 4 .
Technical conditions for corrosion measurements. Electrochemical measurements conditions. EIS experiments were performed at measured EOCP using a sinusoidal voltage signal of 10 mV peak to peak. The analysis was carried out in the frequency range of 0.1 Hz to 100 kHz. The PDP test was performed using a potential range of − 250 to + 250 mV versus SCE at EOCP with a sweep rate of 0.1 mV s −1 . Each test was replicated at least three times to ensure reproducible results. The experimental data were analyzed using Echem Analyst 6.0 software.
Gravimetric study conditions. The calculated average values of low carbon steel (LCS) coupons were achieved by immersion of steel samples into 0.5 M H 2 SO 4 using calculated concentrations of APPH for different periods at 303 ± 2 K. LCS coupons were removed after a specific amount of time, rinsed with distilled water and acetone, and then dried in a low oven before being reweighed. Using mathematical relationships, the corrosion rate, C R (mg cm −2 h −1 ), and inhibition efficiency (IE) were determined from the weight loss of the examined LCS coupons using equations (1, 2): where C R0 and C R are the corrosion rates of LCS due to the dissolution in 0.5M H 2 SO 4 mixed with calculated concentrations of APPH, respectively.
Surface study. LCS samples were exposed to 0.5 M H 2 SO 4 containing calculated concentrations of APPH.
After removing the samples from the corrosive solution and drying it, the surface morphology and structure were investigated using a scan electron microscope (SEM lined to energy dispersive X-ray (EDX) spectroscopy Adsorption isotherm and determination of adsorption thermodynamics parameters. The mechanism by which organic inhibitors attach to the LCS surface is discussed in the adsorption isotherm. Fitting the linear isotherm models (Frendlich, Langmuir, Frumkim, Tempkin, and Flory Huggins isotherm models) expressed in linear equations with the corrosion rate (C R ) and the percentage of Ɵ of the APPH using the following Eqs. Freundlish adsorption isotherm (Eq. 6): Flory-Huggins adsorption isotherm (Eq. 7): El-Awady's thermodynamic/kinetic adsorption isotherm model (Eq. 9): Change of adsorption Gibb's free energy (ΔG ads ) is expressed in Equation (10) and was used to clarify the ability and nature of the adsorption. K ads is a constant of the adsorption equilibrium that was achieved from the isotherm models.

Results and discussions
Weight loss measurements. The effects of APPH concentration on steel LCS corrosion are shown in Table 1. According to the findings, adding APPH to 0.5 M H 2 SO 4 dramatically reduces the corrosion rate (C R ) of LCS while increasing the IE%. In the presence of APPH, a maximum IE of 92% was obtained at 0.5mM. Adding a higher concentration of APPH had no discernible effect on inhibition efficiencies above the used concentrations. As a result, 0.5 mM is chosen as the optimum concentration and used in subsequent immersion time studies. The enhanced performance of APPH at very low concentrations may be attributable to the hydrazide group's interaction with the steel surface through N or O atom and NH 2 .
Electrochemical study. Tafel extrapolation technique. Figure 1 displays the polarization graphs of LCS in 0.5 M H 2 SO 4 with different APPH concentrations. The electrochemical properties are summarized in Table 1. The findings indicated that the APPH molecule is an effective corrosion inhibitor since it demonstrated a steady www.nature.com/scientificreports/ decrease in corrosion current density relative to APPH concentration while increasing inhibition efficiency. The fact that all of the displacements are less than 85 mV and that E corr is minimally shifted shows that the APPH molecule functions as a mixed-type inhibitor 52,53 . Table 2 shows that the inhibitory efficiency of APPH varies from 45 to 79% as concentration increases, with 0.5 mM being the ideal concentration. Further evidence that the APPH compound works as a corrosion prevention agent by lowering the polarization potential came from the reduction in Tafel slopes data from the cathodic and anodic areas. While reducing hydrogen evolution at the cathodic site, the Tafel slopes, on the other hand, have validated metal oxidation at the anodic site [54][55][56] . Additionally, because the values of i corr and C R decreased, the Tafel slopes without inhibitor values were larger than those cited in the absence of APPH.
where M is the equivalent molar weight of iron, i corr is the corrosion current density (A cm −2 ), t is the immersion time (s), and F is the Faraday constant 57 .
(11)  www.nature.com/scientificreports/ Measurements made using EIS. EIS is a supplemental method for testing the affectivity of APPH, which is used to cover the surface of LCS in 0.5 M H 2 SO 4 and to clarify the surface chemistry and kinetic properties of the LCS/electrolyte interface processes. Diverse corrosion systems, such as charge transfer regulation, diffusion control, or a mixed type, may exhibit different characteristics in their EIS analysis. EIS data is typically converted into equivalent electrical circuits in practice, which are then used to categorize the electrical properties of the electrochemical boundary. One of these circuits is the constant phase element model (CPE) 58 , which is broken down into three components CPE, solution resistance (Rs), and charge transfer resistance (R ct ) (Fig. 2). No nature effect of impedance diagrams with the presence of APPH with and without 100 mM KI compared with 0.5 M H 2 SO 4 ; accordingly, the existence of APPH does not affect the corrosion mechanism ( Table 3). The Nyquist grave and bode plot lines grave for LCS in 0.5 M H 2 SO 4 electrolyte at calculated quantities of APPH are depicted in Fig. 3a,b. The observed single depressed capacity semicircles on the obtained plots for the LCS/ electrolyte interface in the analyzed sulfuric acid environments with and without varied APPH amounts suggest that a charge transfer mechanism structures the corrosion behavior on the surface of LCS. The protective layer and adsorption formation at the LCS-electrolyte interface are connected to how the size of the Nyquist semicircle changes as APPH concentration increases 59 .

Synergism consideration.
When the combined effect of multiple compounds is greater than the sum of the activities of the individual compounds, this is known as the synergistic effect of APPH inhibitors. For the purpose of determining the synergism parameter (S), the formula that follows should be utilized as in equation (12).
where η 1 is the inhibitory action of iodide, η 2 is the IE of the APPH and η ′ 1+2 is IE of iodide + APPH. The values of S are calculated as 1.81, 1.79, 1.83 and 1.81 with respect to 0.1, 0.2, 0.4 and 0.5 Mm APPH, respectively, which are more than unity, showing that the enhanced IE is also a function of KI 60 . Addition KI into 0.5 M H 2 SO 4 corrosive media, I − anion quickly absorbs into the anodic area of the LCS; thus, the positive excess charge on the anodic area of the steel surface is reduced, and the surface will be negatively charged. Accordingly, the protonated APPH is attracted to the negative surface of the steel, forming a protective layer through physical adsorption. Figure 2. An inhibited system's equivalent electrical circuit (CPE) with an inhibited system. The previous investigation approves the shift in corrosion potential to a less negative value; thus, the inhibition in the case of adding KI is an anodic inhibitor (Tables 2, 3; Fig. 4).

The influence of exposure duration on the corrosion behavior of LCS in 0.5 M H 2 SO 4 .
In the absence of APPH, an increase in the immersion time to 1, 2, and 6 h led to an increase in the corrosion of the LCS, as shown by an increase in the values of i corr and a decrease in the values of R p . This was confirmed by the fact that the values of i corr increased while the R p values decreased (Fig. 5). This is due to the fact that prolonging the duration of immersion results in a greater degree of LCS being dissolved by the caustic action of 0.5 M H 2 SO 4 solution. According to some reports, the cathodic reaction for metals and alloys in H 2 SO 4 solutions is the hydrogen evolution, which results in the consumption of electrons at the cathode. The increase in the anodic currents with potential and with the increase in immersion time indicates that increasing the applied voltage in a less negative direction makes it easier for steel to corrode 61 . The reduction in the corrosion parameters for the LCS was due to the inclusion of APPH. Whereas, the i corr values go down while the R p and IE% values go up when there is an increase in the amount of APPH present as well as when the exposure period of the LCS goes up from 0 to 6 h before the electrochemical measurements are taken. This was further corroborated by the electrochemical results shown in Table 3, which demonstrates that APPH is a good corrosion inhibitor for the LCS when immersed in a solution containing 0.5 M H 2 SO 4 and its effectiveness rises with the increase of immersion time.
Surface study. FTIR spectra were analyzed so that researchers could better understand the interaction of APPH molecules with the steel surface. Figure 6 displays the infrared (FTIR) spectra of pure APPH as well as scrapped samples collected from LCS surfaces following corrosion experiments conducted in the presence of APPH. It was discovered that the peaks that appear in the spectrum of pure APPH do not appear in the scrapped samples' spectra in the same way. The N-H stretching frequencies for APPH were observed to be at 3377 cm −1 , the C=C stretching frequencies for individual APPH were recorded to be at 1612 cm −1 , and almost completely disappeared with a noticeable reduction in peak integration in the scrapped sample. The stretching frequencies of the C-H, C-O group, almost disappeared in the scrapped sample. The surface morphology of the corroded coupon was characterized with the aid of SEM after immersion in 0.5 M H 2 SO 4 solution and is a function of 0.5 mM APPH and in the case of adding 100 mM KI. The surface images presented in Fig. 7 are indicated that the surface of LCS before and after immersion in 0.5 M H 2 SO 4 solution while LCS, which corroded in 0.5M H 2 SO 4 , exhibit a more severe grain border attack than the presence of 0.5M H 2 SO 4 (Fig 7a,b). The attack is more extreme in the case of addition APPH (Fig. 7c) than in the addition of  www.nature.com/scientificreports/ and the activities that they perform. The chemical reactivity of the APPH inhibitor can be anticipated by using this method, which involves conducting an analysis of the quantum chemical indices. According to the frontier orbital theory, the reaction that takes place between reactants typically takes place on the HOMO and LUMO, and the creation of a transition state is controlled by an interaction that takes place between the frontier orbitals of the reactants. As a consequence of this, analyzing the distribution of HOMO and LUMO was necessary to discover the inhibition mechanism. On the one hand, the unoccupied d orbitals of the Fe atom have the ability to accept electrons 42,44,62,63 . Equations (13)(14)(15)(16)(17)(18)(19) provide a summary of the computed quantum descriptors, which include E HOMO , E LUMO , E HOMO − E LUMO energy gap (ΔE), dipole moment (μ) and total energy (TE), electronegativity (χ), electron affinity (A), global hardness (η), softness (σ), ionization potential (I). The overall electrophilicity,  Because APPH molecule contains hetero-atoms (N and O), a hydrazide group, and a benzene ring in addition to a benzene ring and is resonant on the whole APPH inhibitor molecule, the APPH corrosion inhibitor molecule has unique properties in terms of stability as well as the sensitivity of APPH molecule to the formation of coordination bonds with the LCS surface. These properties are due to the fact that APPH molecule is resonant on the whole inhibitor molecule. In the case of APPH molecule, HOMO and LUMO were investigated, and the results are presented in Fig. 8. Table 4 contains a listing of the E, μ and χ, and values that were calculated for the criterion energy of frontier molecular electrons. HOMO is the theory that describes how the contribution electrons of APPH molecule have an effect. It should come as no surprise that APPH molecule include more  www.nature.com/scientificreports/ electrons. E HOMO is a marker for inhibitive action and serves as a signal. Because APPH molecule also contains O and N in addition to the hydrazide group, the APPH particles used as a corrosion inhibitor have the ability to donate unshared pairs of electrons to the free orbitals of iron atoms, which are referred to as d-orbitals. A better explanation of LUMO could be found in the affinity calculations performed on APPH molecule. On the other hand, E is also an important quantity that specifies the bonding of APPH to the steel surface. A smaller value for E was associated with a more significant degree of inhibition in most cases. According to Table 4, APPH has an E value equal to 0.1372 eV. APPH has a minimal value of χ, demonstrating that it is quite effective at inhibiting activity. In this investigation, the value of χ supported the methodological findings. The high value of μ indicated that the corrosion inhibitor was superior to the others. According to the findings of this research, the value of the dipole moment μ of APPH molecules was 5.8158, which indicates that the APPH molecules have effective inhibitory control. As seen above, APPH molecules can adsorb on the LCS surface by exchanging water for more APPH molecule 5,64-67 .
The HOMO/LUMO for APPH showed that the HOMO orbital was localized on pyridine, but the LUMO orbital was switched to the benzene ring. DFT studies 65 were used to estimate hardness and softness values. The APPH has a value of 0.0686, indicating that APPH as a corrosion inhibitor is expected to be a perfect inhibitor. APPH molecules have a chemical softness of 14.57, indicating that they have a higher inhibition efficiency 66 .
The calculations for HOMO and LUMO on APPH showed that the HOMO orbital was situated on the pyridine atom, whilst the LUMO orbital was moved to the benzene ring. This was discovered by comparing the two orbitals. To make estimations about the values of hardness and softness, DFT research was applied 65 . In light of the fact that the APPH has a value of 0.0686, one can conclude that the APPH, when employed as a corrosion inhibitor, ought to perform at the level of an ideal inhibitor. The chemical softness of APPH molecules is 14.57, which implies that they are more effective in suppressing activity than other molecules 66 .
Adsorption isotherms. Figures 9 illustrates the different adsorption models that were investigated in this study. To choose the most suitable model, we considered the R 2 values presented in Table 5 for each isotherm model. The data were compatible with the isotherms of Langmuir, Flory-Huggins, and Temkin, but the Langmuir isotherm offered the best fit for the data. The Langmuir isotherm, which has R 2 values of 0.99, provides the most accurate description of the adsorption mechanism of APPH on LCS in a medium of sulfuric acid. As a consequence of this finding, the Langmuir adsorption isotherm is an appropriate tool for determining the adsorption equilibrium constant (K ads ). Table 6 reported the Gibb's free energy change of adsorption (ΔG ads ) at room temperature. The ΔG ads of APPH as LCS corrosion inhibitor is negative and have value of 33.3 kJ/mol. This finding suggests that the APPH adsorption on the LCS surface occurred spontaneously, was possible, and instead followed the physical adsorption mechanism (Fig. 10).
When a metallic substrate is positively charged in H 2 SO 4 , many published works have shown that chloride ions and negative species first adsorb onto the surface of the substrate. Because of this, the negatively charged surface that was produced as a result is what makes the adsorption of protonated APPH possible via electrostatic attraction. It is important to point out that the protonation of the amino-functional group found in APPH results in a favorable state in H 2 SO 4 . Consequently, following the initial adsorption of I 1− and SO 4 2− species, the protonated APPH will adsorb via electrostatic contact on the first created layer of the negative species. This will occur after the initial adsorption of I 1− and SO 4 2− species. As mentioned earlier, APPH is considered a mixed adsorption inhibitor, which suggests that it inhibits both physisorption and chemisorption. Other un-protonated APPH induces coordination interactions with d empty molecular orbitals of metal, in addition to the apparent physical adsorption of the protonated molecule. Figure 10 shows a diagrammatic representation of the adsorption process in its basic form. Koumya et al. 67 made observations that were very similar to these ones.

Data availability
This article contains all of the data that was generated or processed while this study was being conducted, and it was published. It is recommended that anyone who is interested in requesting data from this study get in touch with Professor Dr. A. El Nemr.